The goal of this proposal is to study the activation mechanism of the FSH receptor (FSH-R). In Aim 1, the C-terminal residues of the FSH-a subunit will be examined to determine conclusively which amino acid(s) is involved in receptor activation, which might be involved in receptor binding, and what the structural and functional relationships of these amino acids are. In Aim 2, the C-terminal half of the FSH-R will be investigated to identify the amino acid residues that are responsible for receptor activation and to determine their roles in receptor activation. In Aim 3, the high affinity hormone contact points in the N-terminal half will be identified and the role of amino acids in hormone binding determined.